The invention concerns a procedure for the determination of active code sequences, in particular, of identification sequences (midambles) in mobile radio systems, especially for the TDD-Mode of the Standards 3GPP.
The employment of Time Division Duplex (TDD) for the uplink (connection of the mobile station to the base station) and the downlink (connection of the base station to the mobile station) for various mobile radio standards has been made known, for example, by T. Ojanperä, R. Prasad “Wideband CDMA for Third Generation Mobile Communications”, Artech House, 1998, ISBN 0-89006-735-X, Pages 261 to 277. Therein, a TDD Modus is presented, in which each downlink and uplink slot of the TDD framework is split up into a plurality of code channels with an orthogonal spreading code. Each code channel comprises a first data zone, a second data zone and an identification sequence (midamble) placed between the said data zones. Although the data chip sequences, because of multiplication with orthogonal spreading codes, are orthogonal to one another, the identification sequences (midambles) are not orthogonal to each other.
In certain operational situations checks must be made, to see which identification sequences (midambles) are active. Fundamentally, this could be done by correlation of the received data sequence in the midamble area, inclusive of all allowable midambles (identification sequences). By the squaring of the correlation-coefficients, a capacity centered evaluation can be achieved. If the square of a defined correlation coefficient, in relation to the entire capacity of the sum of the midambles oversteps in a logarithmic scale a certain threshold, then the conclusion could rest on an active midamble, and hence on an active code channel. This procedure adapts itself, however, only to the detection of the active midambles, providing that the midamble-code-sequences exhibit a satisfactory cross-correlation characteristic. In the case of short midamble-code-sequences and a high degree of disturbance, then, because of the poor cross correlation characteristics, erroneous or failed detection comes to the fore, because no clear-cut threshold can be found, which separates a valid hypothesis from a faulty hypothesis.
All references cited herein are incorporated herein by reference in their entireties.